The term polyurethane refers to the class of chemical compounds obtained by the reaction of a polyisocyanate with materials containing hydroxyl groups such as polyesters, polyethers, or glycols. Foamed polyurethane materials are generally formed by the reaction of a polyhydroxyl compound ("polyol"), with a polyisocyanate in the presence of a foaming agent. The term polyurethane, as used herein, also refers to polymers containing urea groups resulting from the polyisocyanate reaction with amines or water ("polyisocyanurates"). Rigid polyurethane foams are widely used in the construction and building industries. They are easily molded, sprayed, or cast onto steel, glass-reinforced plastics, or other parts where they protect valuable machinery, or other wear-prone surfaces. They can also be used as synthetic woods, baffles, or as core material for hollow structures such as airplane wings and wall panels. Rigid polyurethane foams provide abrasion and corrosion resistance, high tensile, compression and tear strength, and oil and solvent resistance.
A well-recognized problem with polyurethane foams, however, is the flammable nature of polyurethanes. Not only are polyurethanes generally highly flammable, but the gases given off during combustion ca be highly toxic. The prior art is replete with attempts at making polyurethane foams more fire resistant. Most such methods entail incorporating fire retardant additives into the foam and/or covering the foam with a fire retardant coating. None of the prior art methods are wholly satisfactory. Such methods tend to impair the physical properties of the foam, and/or they tend to drive up the cost of manufacturing the foam.
There is, therefore, a need for a fire retardant polyurethane foam which has substantially the same physical properties as ordinary foams.
There is also a need for a fire retardant polyurethane foam which will not be substantially more expensive to manufacture than ordinary foams.